Wet-laid nonwoven sheets of synthetic polymeric fibrids and short length staple fibers are known from U.S. Pat. No. 2,999,788. As taught in said patent, the fibrids are prepared by shear precipitation of solutions of the polymer, preferably in an aqueous medium which extracts the polymer solvent and causes the polymer to come out of solution. Generally, the fibrids are readily converted into paper by paper-forming techniques similar to those employed with wood pulp.
Activated carbon is well-known to be useful in removing impurities from air, water and solvents because of its very high microporous surface area (&gt;500 m.sup.2 /g). In large industrial systems, beds of loose carbon are commonly used for removing impurities from gaseous and liquid streams. In smaller operations, fibrous systems (e.g. felts, papers) in which carbon is mechanically entrained or adhesively attached, are often used.
Fibrous systems employing mechanically entrapped carbon particles are invariably "dirty". That is, the fibrous matrix sheds small particles when pulsed, shaken, or "worked". The shed particles are messy and can interfere with electrical equipment because they are conductive.
To help alleviate the shedding problem, low porosity fibrous sheets can be bonded to the face of the fibrous system or the fibrous system can be impregnated with a resin. These methods increase the pressure drop needed to maintain flow and do not completely solve the shedding problem, especially if the fibrous system is vigorously worked.
Non-shedding, high porosity structures can be obtained by affixing carbon particles to the fibers of high-loft non-wovens with an adhesive. However, the adhesive reduces the activity of the carbon. Also, the method is suitable only for a highly open porous fiber matrix wherein the carbon particles can penetrate into the center of the structure.
The present invention deals with the aforementioned problems.